PrintWriter add text to file

In my online computer science class I have to write a program to determine the surface gravity on each planet in the solar system. I have gotten almost every aspect of it to work save one. I need to write the surface gravity to a file using a separate method. This is my current method:

public static void writeResultsToFile(double g) throws IOException{

PrintWriter outFile = new PrintWriter(new File("planetaryData.txt"));

outFile.printf("%.2f%n", g);
outFile.close();
}

My problem is that when I write it to a file it will overwrite the previous value. How do I get it include all of the values. Here is the entirety of my code if that helps: